1. Field of the Invention
The present invention relates to a roundness measuring apparatus. In particular, the invention relates to a roundness measuring apparatus that is capable of changing a stylus automatically.
2. Description of the Related Art
A roundness measuring apparatus is known as an instrument for measuring the roundness of a measurement target object. A roundness measuring apparatus is provided with a base, a turntable, a column, an elevation slider, a sliding arm, and a detector. The turntable is provided on the base. The turntable can rotate around a vertical axis. A measurement target object is placed on the upper surface of the turntable. The column stands on the base. The elevation slider can move upward and downward along the column. The sliding arm is provided on the elevation slider. The sliding arm can slide in the direction orthogonal to the vertical axis. The detector is mounted at the tip of the sliding arm. The detector detects the displacement of a stylus, which is brought into contact with the measurement target object, and outputs the detected stylus displacement in the form of an electric signal. An example of such a roundness measuring apparatus of related art is disclosed in Japanese Unexamined Patent Application Publication No. 2004-233131.
A roundness measuring apparatus typically comes with a plurality of styli having various shapes, which are designed to fit various shapes of measurement sites (e.g., parts or regions) of a measurement target object. Therefore, when a user uses a roundness measuring apparatus for measurement, they replace its stylus with one that is appropriately suited for the shape of a measurement site of a measurement target object before measurement. For example, when the roundness of a deep hole of a measurement target object is measured, they replace its stylus with a deep-hole stylus, which has a great stylus length, before measurement. When roundness inside a groove is measured, they replace its stylus with a groove stylus and then carry out measurement. In the related art, a person who carries out measurement changes a stylus. For stylus replacement, a person who carries out measurement has to stop measurement work. After removing a stylus that is currently in use from a detector, he or she attaches a different stylus to the detector. Then, he or she resumes measurement work.
In such stylus replacement of the related art, it is necessary for a person who carries out measurement to stop measurement work and manually remove a current stylus from a detector and manually attach a different stylus to the detector. Therefore, it involves considerable downtime in measurement work, that is, a long time period throughout which measurement work has to be stopped. In addition, the burden of manual stylus removal and attachment that is placed on the person who carries out measurement is not light. A conceivable solution to the above problem is to apply an automatic probe changer, which is used in the field of a three-dimensional measuring apparatus and the like, to a roundness measuring apparatus. That is, it is conceivable to provide a stylus stock unit that stores plural types of styli on a roundness measuring apparatus.
However, if a stylus stock unit that stores plural types of styli is provided on a roundness measuring apparatus, a measurement region will be very restricted because it is necessary to provide the stylus stock unit over a turntable, which constitutes the measurement region.